Add system_note_metadata model

app/models/note.rb

@@ -37,6 +37,7 @@ class Note < ActiveRecord::Base
 
   has_many :todos, dependent: :destroy
   has_many :events, as: :target, dependent: :destroy
+  has_one :system_note_metadata, dependent: :destroy
 
   delegate :gfm_reference, :local_reference, to: :noteable
   delegate :name, to: :project, prefix: true
@@ -70,7 +71,9 @@ class Note < ActiveRecord::Base
   scope :fresh, ->{ order(created_at: :asc, id: :asc) }
   scope :inc_author_project, ->{ includes(:project, :author) }
   scope :inc_author, ->{ includes(:author) }
-  scope :inc_relations_for_view, ->{ includes(:project, :author, :updated_by, :resolved_by, :award_emoji) }
+  scope :inc_relations_for_view, -> do
+    includes(:project, :author, :updated_by, :resolved_by, :award_emoji, :system_note_metadata)
+  end
 
   scope :diff_notes, ->{ where(type: %w(LegacyDiffNote DiffNote)) }
   scope :non_diff_notes, ->{ where(type: ['Note', nil]) }

app/models/system_note_metadata.rb

+class SystemNoteMetadata < ActiveRecord::Base
+  ICON_TYPES = %w[
+    commit merge confidentiality status label assignee cross_reference
+    title time_tracking branch milestone discussion task moved
+  ].freeze
+
+  validates :note, presence: true
+  validates :icon, inclusion: ICON_TYPES, allow_nil: true
+
+  belongs_to :note
+end

config/initializers/0_inflections.rb

@@ -10,5 +10,5 @@
 # end
 #
 ActiveSupport::Inflector.inflections do |inflect|
-  inflect.uncountable %w(award_emoji project_statistics)
+  inflect.uncountable %w(award_emoji project_statistics system_note_metadata)
 end

db/migrate/20170314082049_create_system_note_metadata.rb

+class CreateSystemNoteMetadata < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  def change
+    create_table :system_note_metadata do |t|
+      t.references :note, null: false
+      t.integer :commit_count
+      t.string :icon
+
+      t.timestamps null: false
+    end
+
+    add_concurrent_foreign_key :system_note_metadata, :notes, column: :note_id, on_delete: :cascade
+  end
+end

db/schema.rb

@@ -1075,6 +1075,14 @@ ActiveRecord::Schema.define(version: 20170317203554) do
 
   add_index "subscriptions", ["subscribable_id", "subscribable_type", "user_id", "project_id"], name: "index_subscriptions_on_subscribable_and_user_id_and_project_id", unique: true, using: :btree
 
+  create_table "system_note_metadata", force: :cascade do |t|
+    t.integer "note_id", null: false
+    t.integer "commit_count"
+    t.string "icon"
+    t.datetime "created_at", null: false
+    t.datetime "updated_at", null: false
+  end
+
   create_table "taggings", force: :cascade do |t|
     t.integer "tag_id"
     t.integer "taggable_id"
@@ -1308,6 +1316,7 @@ ActiveRecord::Schema.define(version: 20170317203554) do
   add_foreign_key "protected_branch_merge_access_levels", "protected_branches"
   add_foreign_key "protected_branch_push_access_levels", "protected_branches"
   add_foreign_key "subscriptions", "projects", on_delete: :cascade
+  add_foreign_key "system_note_metadata", "notes", name: "fk_d83a918cb1", on_delete: :cascade
   add_foreign_key "timelogs", "issues", name: "fk_timelogs_issues_issue_id", on_delete: :cascade
   add_foreign_key "timelogs", "merge_requests", name: "fk_timelogs_merge_requests_merge_request_id", on_delete: :cascade
   add_foreign_key "trending_projects", "projects", on_delete: :cascade

spec/factories/system_note_metadata.rb

+FactoryGirl.define do
+  factory :system_note_metadata do
+    note
+    icon 'merge'
+  end
+end

spec/models/note_spec.rb

@@ -9,6 +9,7 @@ describe Note, models: true do
     it { is_expected.to belong_to(:author).class_name('User') }
 
     it { is_expected.to have_many(:todos).dependent(:destroy) }
+    it { is_expected.to have_one(:system_note_metadata).dependent(:destroy) }
   end
 
   describe 'modules' do

spec/models/system_note_metadata_spec.rb

+require 'spec_helper'
+
+describe SystemNoteMetadata, models: true do
+  describe 'associations' do
+    it { is_expected.to belong_to(:note) }
+  end
+
+  describe 'validation' do
+    it { is_expected.to validate_presence_of(:note) }
+
+    context 'when icon type is invalid' do
+      subject do
+        build(:system_note_metadata, note: build(:note), icon: 'invalid_type' )
+      end
+
+      it { is_expected.to be_invalid }
+    end
+
+    context 'when icon type is valid' do
+      subject do
+        build(:system_note_metadata, note: build(:note), icon: 'merge' )
+      end
+
+      it { is_expected.to be_valid }
+    end
+  end
+end